The US government viewed the UN Secretary-General as “very willing” to serve Russian interests, according to new revelations from classified documents leaked online. The records show that Washington was closely monitoring Antonio Guterres.

Several documents describe private communications involving Mr Guterres and his deputy, Amina Mohamed. It is the latest in a series of leaked classified documents that US officials are trying to piece together.

The documents contain remarks by Mr Guterres on the war in Ukraine and a number of African leaders. A leaked document focuses on the Black Sea grain deal brokered by the UN and Turkey in July after fears of a global food crisis.

It suggests that Mr Guterres was so keen to preserve the deal that he would not hesitate to serve Russia’s interests. His actions in February, according to the assessment, “undermined broader efforts to hold Moscow accountable for its actions in Ukraine.”

UN officials were troubled by the suggestion that the world’s top diplomat was soft on Moscow. Declining to comment on the leaked documents, a senior official said the UN was “driven by the need to mitigate the impact of war on the world’s poorest”. “This means we must do everything we can to reduce the price of food,” he added, “and ensure that fertilizers are accessible to the countries that need them most.”

Russia has often complained that its own grain and fertilizer exports are adversely affected by international sanctions and has threatened at least twice to suspend cooperation with BSGI if its concerns are not addressed. Russian grain and fertilizer are not subject to international sanctions, but Russia says it has faced difficulties. UN officials are clearly unhappy with America’s interpretation of Mr Guterres’ efforts and say the secretary-general has made clear his opposition to Russia’s war.

Another document from mid-February describes a frank discussion between Mr Guterres and his deputy, Amina Mohamed. In it, Mr Guterres expresses “disgust” at EU Commission President Ursula von der Leyen’s call for Europe to produce more weapons and ammunition as a result of the war in Ukraine. The two also talk about the recent summit of African leaders. Amina Mohammed says Kenyan President William Ruto is “rogue” and she “doesn’t trust him”.

America is known to be among a number of nations that routinely spy on the UN – but when the products of that spying come to light, they are extremely disturbing and, for the world’s top diplomat, potentially damaging.

US national security spokesman John Kirby told the BBC that the US government was trying to get to the bottom of the leak. “This is a series of dangerous leaks. We don’t know who is responsible, we don’t know why. And we’re assessing the national security implications, and there’s also a criminal investigation going on right now,” he said during President Joe Biden’s trip to Belfast on Wednesday.